Antibacterial oxide semiconductors, such as titanium oxides, zinc oxides, tungsten oxides, and iron oxides, which have high photocatalytic activity and excellent durability, have been introduced as various fixed-type photoreactors that are immobilized on fixed supporters. For instance, Japanese Laid-Open Patent No. 63-97234/1988 discloses an immobilized photocatalyst comprised of particle-, flake-, or fiber-shaped clear material coated with a platinum- or palladium-doped titanium oxide thin film.
The development of a product bearing a photocatalyst with a higher photoreactivity is greatly desired because it broadens the possibility of using such a product as an antipollution material, besides acting as an antibacterial agent.
Among various photocatalytic materials, titanium oxide, which has the highest photocatalytic activity and excellent durability, already has been actually used as an antibacterial agent in a particulate form. Titanium oxide, however, can be excited only by ultraviolet light, the amount of which is limited under actual usage conditions. Accordingly, it can be said that the window glass application for indoor use is best suited for the product, as both artificial illumination and sunlight can be utilized.
However, as the window glass application also requires high clarity of photocatalytic film, titanium oxide particulate-based material does not be utilized. Thus, achieving a photocatalytic film with both high photocatalytic activity and clarity can maximize its performance and significantly broaden potential applications.
Another serious problem with photocatalytic film in window glass application is its significantly reduced reactivity due to Na ion diffusion from the soda-lime glass base material. As a solution to this problem, the use of a Na diffusion-preventing silica undercoat for glass surfaces has been proposed (Paz, et al., J. Mater. Res., Vol. 10, p2842, 1995). It has been reported that this method can achieve photocatalytic activity similar to that of a titanium oxide film coating on a quartz substrate.
Recently, in the field of semiconductors, reduced yield caused by trace organic gases in clean rooms being deposited on substrates has become a serious problem as the density of elements increases. In addition, even in a residential setting, allergic reactions to various plasticizers that may be in construction materials, such as formaldehyde and acetaldehyde, have become a serious concern.
The aforementioned photocatalysts, such as titanium oxide, effectively oxidize organic materials, and can decompose various organic gases existing indoors. Therefore, the photocatalysts have the potential of becoming a key material to solve the above-mentioned reduced semiconductor yield and allergy problems.
However, for a photocatalyst to decompose organic gases, it is essential to improve its reactivity and expand its surface area because the concentration of gases is extremely small.
In the past, various attempts were made to make shoji-screen paper- or glass fiber cloth-based material bear a photocatalyst to decompose organic gases of extremely low concentration (for instance, Japanese Laid-Open Patent No. 1-139139/1989). Although the surface area is large, shoji-screen paper is an organic material itself that, over time, inevitably deteriorates and possibly becomes a new pollutant. This limits the scope of application. Moreover, a photocatalyst directly borne by a glass fiber cloth cannot achieve a high level of photocatalytic activity. This is because alkaline components diffused from the glass reduce the photocatalyst's crystallization property during the process of stabilizing the photocatalyst on the glass fiber.
Accordingly, it is an object of the present invention to provide a photocatalyst that has a higher photoreactivity efficiency and durability, as compared to conventional photocatalysts, a photocatalyst bearing material, and a manufacturing method of the photocatalyst.
Another object of the present invention is to provide a photocatalyst that solves the aforementioned problems of conventional techniques, a photocatalyst bearing material, and a manufacturing method of the photocatalyst.
Yet another object of the present invention is to maintain a high photocatalytic activity even when a base material comprised of alkaline-containing glass composition is used so as to perform excellently in indoor air cleaning, antibacterial and defogging action in offices, hospitals, automobiles and the like.
Furthermore, an object of the present invention is to provide a photocatalyst and a photocatalyst bearing material that solve the aforementioned problems with conventional techniques, and that not only efficiently decompose harmful organic gases, but also have antibacterial, anti-fouling, and defogging functions, when the photocatalyst and the photocatalyst bearing material are used as air cleaning for super clean enclosed space for semiconductor production, conveyance enclosed spaces, clean rooms for various other purposes, office buildings, and automobiles, and are used as interior wall material, window glass, and in air filters. In addition, an object of the present invention is to provide a manufacturing method for the aforementioned photocatalyst and the photocatalyst bearing material.